Tabular silver halide grains are crystal possessing two major faces that are substantially parallel in which the average diameter of said faces is at least three times (and often more times) the distance separating them.
Silver halide photographic emulsions containing a high proportion of tabular grains have advantages of good developability, improved covering power and increased useful adsorption of sensitizing dye per weight of silver due to their high surface area-to-volume ratio. The use of such emulsions in photographic materials is disclosed in U.S. Pat. Nos. 4,425,425, 4,433,048, 4,435,499, 4,439,520, and other related patents.
However, photographic materials containing tabular silver halide grains also have certain disadvantages. One of these is that they tend to easily fog under high temperature accelerated processing. Therefore, tabular silver halide grains are not satisfactory for use in photographic emulsions required to have high sensitivity and low fog.
It is known to incorporate various additives, such as stabilizers and antifoggants, in ordinary light-sensitive silver halide photographic materials for minimizing the rise of fog in dependence of the development processing conditions. For example, nitrobenzimidazoles, mercaptothiazoles, benzotriazoles, nitrobenzotriazoles, mercaptotetrazoles, etc., are described as such additives in E.J. Birr, Stabilization of Photographic Silver Halide Emulsions, Focal Press, and in U.S. Pat. Nos. 3,954,474, 3,982,974, etc. However, while these additives can depress an increase of fog in a light-sensitive silver halide photographic material containing tabular grains during high temperature processing to some extent, a remarkable decrease in sensitivity cannot be prevented.
For example, it is known to use light-sensitive silver halide photographic materials in high-temperature development processing using automatic developing machines. In order to enhance the physical strength of the photographic materials during the development at high temperature and in automatic developing machines and prevent them from becoming physically fragile it is known to conduct the processing with an aldehyde hardener in the developing solution. However, a developing process with a developing solution containing an aldehyde, particularly an aliphatic dihaldehyde, concurrently causes an increase of fog, particularly as the temperature of the developing solution increases. The fog can be depressed to some extent by using strong antifogging agents such as benzotriazole and 1-phenyl-5-mercaptotetrazole in the developing solutions (as described in L.F. Mason, Photographic Processing Chemistry, Focal Press). However, these antifogging agents, when used to develop light-sensitive silver halide photographic materials containing tabular silver halide grains, concurrently depress development and reduce emulsion sensitivity.
Aromatic hydroxy compounds such as .alpha.-naphthol, pyrocatechol, resorcinol, methoxyphenol or naphtholsulphonic acid have been disclosed for preventing latent image regression in DE 1,107,508. 1,3-Dihydroxybenzene carboxylic compounds have been disclosed in U.S. Pat. No. 3,380,828 to prevent stain formation in unhardened silver halide emulsions comprising a developing agent and a hardener precursor for use in rapid processing systems. 2,5- and 3,5-dihydroxybenzene carboxylic acids have been described in DE 1,171,266 to decrease fog in fresh and stored silver halide emulsions. No reference is made in these patents to silver halide emulsions comprising tabular silver halide grains.
Reducing agents, such as chromans, tocopherols, hydrazines, p-phenylenediamines, aldehydes, aminophenols, phenidones, sulfites, H.sub.2 gas, sulphinic acids, di- or trihydroxybenzenes, endiols, oximes and reducing sugars, are disclosed in DE 3,615,336 as added to silver halide emulsions containing tabular grains produced in the presence of an oxidant compound, such as H202, a peroxy-acid salt and O.sub.3. The reducing agent is deactivated or reduced during or after the chemical ripening.